A Garda investigation has begun into the suspicious circumstances behind the cause of a fire inside a block of apartments in Limerick city, Sunday night, writes David Raleigh.

Between 40 to 50 people were evacuated from the Mahon House apartment block, on Upper William Street, after a pile of "rubbish" was discovered burning on a fifth floor internal escape route, reliable sources said.

Limerick City and County Fire and Rescue Service received a 999 alert at around 8pm with a report of smoke seen coming out of windows on the fifth floor.

Fire control dispatched three units to the scene, which is located a few doors from the fire station house, on Mulgrave Street.

A team of firefighters using breathing apparatus entered the building and quickly put out the blaze. Fire crews also searched the building for any potential casualties or persons injured, and went through the premises knocking on doors to make sure those in the apartments were safely evacuated.

There are no reports of any injuries.

Those evacuated later returned inside after the fire service declared the building safe shortly before 9pm.

"There was rubbish alight on the fifth floor on a landing near a stairwell," said a source.

"The smoke had spread along the corridors, but the fire was thankfully put out really quickly."

"There were fire fighters wearing oxygen masks and knocking on doors, and telling people to leave."

"The smoke had filled up to the fifth floor, so the fire fighters used special fans to clear the smoke out of the building," they added.